Step-by-step explanation:
Since the polygon has four vertices (D,E,F and G), it is a quadrilateral (4 vertices).
It’s 4
7-11= 4
3-7= 4
and so on
Hope it helps:)
You just need to plug those expressions inside the formula: it doesn't matter if they're expressions involving a variable instead of plain numbers: the formula becomes

If you want, you can simplify it by expanding the square and then multiply the two parenthesis:
